1. Field of the Invention
The invention relates to a door lock, more particularly to a door lock which cannot be disassembled from the outer side of a door, which is easy to install and which has a deadbolt assembly with a low-cost, corrosion-resistant bolt member.
2. Description of the Related Art
FIG. 1 illustrates a door lock disclosed in U.S. Pat. No. 3,992,908. The door lock is shown to comprise a lock housing assembly (A) and a deadbolt assembly (B). The lock housing assembly (A) is to be installed in a through bore of a door (not shown), while the deadbolt assembly (B) is to be installed in an opening that is at right angles with the through bore of the door.
The lock housing assembly (A) comprises an exterior housing section (A1) with an interior sleeve extension (A11) which has a rear end formed with diametrically opposite notches (A12) that permit the extension of the deadbolt assembly (B) through the sleeve extension (A11). The sleeve extension (A11) is formed with an internal screw thread (A13). The exterior housing section (A1) has a cylindrical chamber that receives an exterior lock cylinder unit (A14) therein. The lock cylinder unit (A14) has a key-operated rotary plug (A15) with a rearwardly projecting spindle (A16).
An interior housing section (A3) may be coupled directly to the exterior housing section (A1) by means of an external screw thread (A31) thereof, or may be coupled indirectly thereto by means of an internally and externally threaded coupling sleeve (A2) which engages the thread (A13) of the sleeve extension (A11) and which further engages the thread (A31) of the interior housing section (A3).
The lock housing assembly (A) further comprises an interior cylindrical insert (A4) adapted to be received in a bore (A32) of an interior housing section (A3). An interior lock cylinder unit (A5) is contained within a chamber of the insert (A4) and has a rotary key-operated plug (A51) with a spindle (A52) that interfits telescopically the spindle (A16).
It is noted that, although the arrangement of the exterior housing section (A1) and the deadbolt assembly (B) can lock the former against rotation, the application of a great amount of torque on the exterior housing section (A1) may result in damage to the door lock, thus facilitating the disassembly of the door lock from the outer side of the door.
FIGS. 2 and 3 illustrate a deadbolt assembly disclosed in U.S. Pat. No. 4,664,433. The deadbolt assembly is shown to comprise a deadbolt casing assembly (C) and a drive arm (D). The casing assembly (C) includes a spaced pair of side plates (C1). The drive arm (D) is disposed between the side plates (C1) and has a first end formed with a cylindrical hub (D1). The cylindrical hub (D1) has two ends mounted rotatably and respectively to the side plates (C1). A pull member (E) has a rearward extension (E1) that extends into the casing assembly (C) and that is formed with a driving hole (E2). The pull member (E) is movable forwardly and rearwardly in the casing assembly (C). The second end (D2) of the drive arm (D) extends into the driving hole (E2). Forward and rearward movement of the pull member (E) occurs when the cylindrical hub (D1) is rotated by a spindle (not shown). A leaf spring (G) extends between the side plates (C1) below the drive arm (D) and defines the forward and rearward positions of the drive arm (D).
The deadbolt assembly further comprises a bolt member (F) with a forward bolt part (F1) and a rearward bolt part (F2). The forward bolt part (F1), which has a closed front end and an open rear end, further has opposite flat sides (Fll) and curved upper and lower sides (F12). The rearward bolt part (F2), which has open front and rear ends, further has a circular cross section and is telescoped by the forward bolt part (F1). The rearward bolt part (F2) is formed integrally with the pull member (E) and telescopes a hardened security bar (F3) at the front portion thereof to provide added security against transverse sawing of the bolt member (F).
The rearward bolt part (F2) has two helical slots (F21, F22) formed therein. A guide pin (F4) extends across the flat sides (F11) of the forward bolt part (F1) and passes through the helical slots (F21, F22). Relative rotation between the bolt parts (F1, F2), as guided by the guide pin (F4), would result in an increase or decrease in the total length of the bolt member (F) so as to attain a longer or shorter standard backset length.
In the bolt member (F), the forward bolt part (F1) is not fitted over the rearward bolt part (F2) to permit relative rotation therebetween. Thus, even when the forward bolt part (F1) is made of stainless steel, the rearward bolt part (F2) is still susceptible to corrosion when the deadbolt assembly is used in humid places. Of course, the bolt parts (F1, F2) may both be made of stainless steel to overcome the above drawback. However, a corresponding increase in the material cost of the bolt member (F) will be incurred.